All I have found so far is in this AK post - http://www.audiokarma.org/forums/showthread.php?t=51943&page=2 which doesn't include the 180 numbers but mentions 35400.

I also have 421-8Hs.

Both have cones stamped 35402.

I wish to know if the cones are legit Altec ones. I can remember seeing an Altec components Table which included later cones that didn't follow the 391 first three number rule but can't locate it now. Any replies are welcome.